Defocused CO 2 laser on equine skin: a histological examination

Summary Reasons for performing study : No studies have been published on effects of treatment with a defocused beam carbon dioxide (CO 2 ) laser on equine skin histology. A better understanding of this will help to define how lasers should be used, in order to reduce potential side effects. Objective : To describe the acute effects of different doses of defocused CO 2 laser, ranging from therapeutic to surgical levels, on equine skin. Methods : Defocused CO 2 laser was administered to the skin in the hamstrings (91 J/cm 2 ), fetlock (137 J/cm 2 ) and loin (450 J/cm 2 ) areas of 13 Standardbred horses. The acute effects on skin histology were examined 90 min after the end of therapy. Results : Mild changes with focal spongiosis and subepidermal clefts were found after 91 J/cm 2 irradiation and more severe changes with diffuse subepidermal clefts after the 137 J/cm 2 dose. A homogeneous eosinophilic acellular zone of dermis and destruction of adnexal structures, and significant thinning of the epidermis was observed after the 450 J/cm 2 dose. Conclusions : The present study indicates acute dose‐dependent changes in equine skin histology after laser treatment. Severe tissue damage was induced using a 450 J/cm 2 dose. Potential relevance : To reduce the potential side effects of defocused CO 2 laser treatment, the laser parameters must be carefully evaluated. Caution should be taken if doses higher than 91 J/cm 2 (16 W, 4 min, and 42 cm 2 ) are used in irradiation of equine skin.